Electroluminescent (EL) lighting has been known in the art for many years as a source of light weight and relatively low power illumination. Because of these attributes, EL lamps are in common use today providing light in, for example, automobiles, airplanes, watches, and laptop computers. Electroluminescent lamps of the current art generally include a layer of phosphor positioned between two electrodes, with at least one of the electrodes being light-transmissive, and a dielectric layer positioned between the electrodes. The dielectric layer enables the lamp's capacitive properties. When a voltage is applied across the electrodes, the phosphor material is activated and emits a light.
It is standard in the art for the translucent electrode to consist of a polyester film sputtered with indium-tin-oxide, which provides a serviceable translucent material with suitable conductive properties for use as an electrode. A disadvantage of the use of this polyester film method, however, is that the final shape and size of the electroluminescent lamp is dictated greatly by the size and shape of manufacturable polyester films sputtered with indium-tin-oxide. Further, a design factor in the use of indium-tin-oxide sputtered films is the need to balance the desired size of electroluminescent area with the electrical resistance (and hence light/power loss) caused by the indium-tin-oxide film required to service that area. Thus, the indium-tin-oxide sputtered films must be manufactured to meet the requirements of the particular lamps they will be used in. This greatly complicates the lamp production process, adding lead times for customized indium-tin-oxide sputtered films and placing general on the size and shape of the lamps that may be produced. Moreover, the use of indium-tin-oxide sputtered films tends to increase manufacturing costs for electroluminescent lamps of nonstandard shape.
It is thus desirable to eliminate the need for conventional electroluminescent polyester film. Screen-printed ink systems have been developed that deposit layers of ink onto a substrate to provide electroluminescent lamps. It is known in the art for the light-transmissive or translucent electrode to consist of a suitable translucent electrical conductor, such as indium-tin-oxide, which is dispersed in a resin. This conductive layer of the Electroluminescent lamp is in electrical contact with an electrode lead or bus bars. It is further standard in the art for the dielectric layer to be comprised of barium-titanate particles suspended in a cellulose-based resin. Particularly with known screen printing techniques for applying the separate layers of electroluminescent lamps, the dielectric layer tends to deposit with pin-holes in the layers or have channels therein because of the granular nature of the barium titanate. Such pin-holes and channels in the dielectric layer may cause breakdown of the capacitive structure of electroluminescent lamp, particularly at the area of the crossover of the light-transmissive electrode lead over the rear electrode. This is due to silver from either the light-transmissive electrode lead or the opaque electrode migrating through the pinholes and channels through the dielectric layer to other electrode lead. This short circuits the electroluminescent lamp and results in electroluminescent lamp failure.
It is accordingly an object of the present invention to configure the electroluminescent lamp system to minimize crossover between the light-transmissive and opaque electrodes. This decreases current leakage and thus increases the efficiency of the capacitor and maintains a sufficiently low capacitive reactance to create a bright electroluminescent lamp
It is another object of the present invention to provide an electroluminescent lamp system that may be directly manufactured to the product.
Electroluminescent lamps in the art typically are manufactured as discrete cells on either rigid or flexible substrates. One known method of fabricating an electroluminescent lamp includes the steps of applying a coating of light-transmissive conductive material, such as indium tin oxide, to a rear surface of polyester film, etching the film to create a pattern, applying a phosphor layer to the conductive material, applying at least one dielectric layer to the phosphor layer, applying a rear electrode to the dielectric layer, and applying an insulating layer to the rear electrode. In order to obtain a colored graphical display, the graphical layers are separately constructed and then the various layers may, for example, be laminated together utilizing heat and pressure. Alternatively, the various layers may be screen printed to each other. When a voltage is applied across the indium tin oxide and the rear electrode, the phosphor material is activated and emits a light which is visible through the polyester film.
Typically, it is not desirable for the entire electroluminescent polyester film to be light emitting. For example, if an electroluminescent lamp is configured to display a word, it is desirable for only the portions of the electroluminescent polyester film corresponding to letters in the word to be light emitting. Accordingly, the indium tin oxide is applied to the polyester film so that only the desired portions of the film will emit light. For example, the entire polyester film may be coated with indium tin oxide, and portions of the indium tin oxide may then be removed with an acid etch to leave behind discrete areas of illumination. Alternatively, an opaque ink may be printed on a front surface of the polyester film to prevent light from being emitted through the entire front surface of the film.
Fabricated electroluminescent lamps often are affixed to products, e.g., signs, and watches, to provide lighting for such products. For example, Electroluminescent lamps typically are utilized to provide illuminated images on display signs. Particularly, and with respect to a display sign, electroluminescent lamps are bonded to the front surface of the display sign so that the light emitted by the phosphor layers of such lamps may be viewed from a position in front of the sign.
Utilizing prefabricated electroluminescent lamps to form an illuminated display sign is tedious. Particularly, each electroluminescent lamp must be formed as a reverse image. For example, when utilizing an electroluminescent lamp to display an illuminated word, e.g., “THE”, it is important that the word be accurate, i.e., be readable from left to right, when viewed from the front of the sign. Accordingly, and until now, it was necessary to apply the indium tin oxide to the polyester film as a reverse image, e.g., as a reverse image of “THE”. The subsequent layers of phosphor, dielectric, and rear electrode then are similarly applied as reverse images. In addition, it is possible that the electroluminescent lamp may become damaged while bonding the electroluminescent lamp to the sign.
A need in the art therefore exists for an electroluminescent system that minimizes failures by reducing areas of cross-over between the front electrode or electrode lead and the rear electrode and/or rear electrode lead. A further need exists for a electroluminescent system that prevents migration of conductive material through the dielectric layer. Further a need exists for such electroluminescent systems to be layered directly to the product.